Thyroid Hormones and Insulin in Adaptation of Animal Performance to Variations in Feed Supply and Ambient Temperatures

Abstract

The relation between environmental temperature, feed intake and productive performance of animals is mentioned and illustrated. In the introduction and following questions are raised. How do we and our animals survive when feed becomes a scarcity and how do the organism adapt to variations in environmental temperatures? What are the possibilities for maintenance of high production when changes in the environmental temperatures exceeds the limits for   the   comfort zone of production?. The purpose of the review is to answer these questions. It is stated that production is a function of metabolic turnover. The regulation of the metabolic processes behind that turnover is reviewed. It is concluded that thyroid hormones and insulin are the major factors mediating the environmental effects on the processes behind growth and other forms of animal production. Work showing that secretion rates and plasma levels of thyroid hormones (T3 and T4) is affected by ambient temperature.  Lactation, pregnancy and nutritional level are reviewed.  It was found that levels of T3 and T4 varies up and down with the adequacy of energy supply and that nutritional level is the dominating factor determining the  secretion  rates of T3 and T4. The relation is important for adaptation to variations in feed supply.